The present invention relates to an end-of-travel device for actuating systems of roller blinds or sun shades, such as shutters, sun awnings, etc.
It is known that in actuating systems for roller blinds (to which reference will be made henceforth for the sake of simplicity, but it being understood that the invention is not limited to this application) for some time automatic end-of-travel devices have been used, namely mechanical or electromechanical devices which cause stoppage of the roller blind when it reaches a predetermined final position.
Many examples of these devices exist in the state of the art. In the patent FR 2,076,529 two gear wheels which advance on associated female screws act on end-of-travel switches (microswitches) displacing flanges which slide coaxially on a smooth portion of the female screws.
In a very similar manner the patent EP 0,371,170 describes actuation of end-of-travel switches by means of gear wheels which advance on associated female screws, where, however, it is the gear wheel itself which acts by means of direct contact on the switch (for this purpose it is chamfered on the contact edge).
These systems, although managing to limit the longitudinal dimensions, do not allow precise adjustment of the end-of-travel stops, resulting in positioning errors of the roller blind. A first cause of error is the sensitivity of the microswitch which is actuated. The commercially available microswitches do not ensure constant operation as regards either the position or the moment of activation, namely they are not always activated at the same moment or in the same position (activation may occur after travelling a third or a half of their total travel path). Moreover, with time their characteristics change. Since the manufacturers of actuating systems use commercially available microswitches, this error cannot be eliminated. On the other hand it is likewise not economically advantageous to produce specific microswitches for this type of application. A second cause of error is the speed with which the microswitch is actuated. This parameter in fact influences the position and the moment of activation. The activation position may be rendered more constant by increasing the speed of actuation of the microswitch.
A commercially known solution is one where end-of-travel microswitches are actuated by gear wheels which advance on associated female screws. In this case, however, the movement of the gear wheels is transferred to the movable part of the microswitch by means of a lever able to multiply the operating speed owing to the different length of its arms. It can be easily understood that the dimensions of the arms of the lever determine directly the performance of the system, but at the same time they are also decisive for the space occupied by the system. However, the dimensions of the actuating system are dependent upon the end-of-travel system, which prevent any shortening thereof. Since the dimensions of the actuating system heavily influence both the practicality of assembly and its cost (production, packaging and storage), it is obvious that this system is not of an optimal nature.